The present invention relates to solid axle suspensions for motor vehicles, more particularly to a straight line linkage mechanism guidably positioned between the frame and a solid axle of a motor vehicle.
The rear axles of vehicles can generally be classified as independent, twist or solid. With a solid axle the two rear-wheels of a vehicle are connected together with some form of a rigid beam, bar or tube so that when one of the wheels encounters an irregularity in the road surface the other wheel is also affected. Most commonly, a solid axle is used at the rear of a rear-wheel drive or four wheel drive motor vehicle, particularly light trucks, the solid axle being xe2x80x9clive axlexe2x80x9d, in the sense that the attached left and right wheels are driven through the axle via a connected drive shaft from the vehicle""s engine.
As exemplified at FIG. 1, a solid axle 10 is mounted to a suspension system which allows the axle to travel vertically as the wheels track over rises and dips on a road (or off-road) surface. In order for the axle to accommodate vertical travel relative to the frame 12 (shown cut-away for clarity), the axle is biasably mounted relative to the frame, as for example including a pair of leaf or coil springs 14 and a pair of shock absorbers 16. In order to provide proper tracking of the axle as it undergoes vertical movement relative to the frame, it is known in the art to employ a track bar linkage 18. A track bar is a rigid metal beam having a pivotal frame attachment 20 at one end, and a pivotal axle attachment 22 at the other end. For a further detailed description of a suspension system associated with a track bar linkage, see U.S. Pat. No. 5,884,925 to Wong.
A deficiency of the track bar is that as the axle moves vertically, the track bar requires that the axle attachment arc pivotally in relation to the frame attachment. One known solution is to replace a track bar linkage with a xe2x80x9cScott-Russellxe2x80x9d linkage mechanism. FIG. 2 shows such a Scott-Russell linkage mechanism 50 associated with a suspension system which is structurally and functionally substantially the same as that described above. The Scott-Russell linkage mechanism 50 includes a rigid beam 52, a connector rod 54 and a link 56. The link 56 is pivotally connected to the axle 58 and to a first end 60 of the beam. A second end 62 of the beam is pivotally connected to the frame 64 (shown cut-away for clarity). The connector rod 54 is pivotally connected between a mid-point location of the beam and a mid-region location of the axle.
FIG. 3 diagrammatically depicts the above described Scott-Russell linkage mechanism 50. The theory of ideal operation of the Scott-Russell linkage mechanism is as follows: since the connector rod 54 is half as long as the beam 52 and since the connector rod is connected to the mid-point of the beam, as the axle 58 moves vertically relative to the frame 64, the first end 60 of the beam 52 would move horizontally, allowing for vertical movement of the axle. However, in practice, the first end 62 is not able to move truly horizontally because of the associated pivoting of the link 56. Accordingly, a Scott-Russell linkage mechanism has a deficiency in that the link 56 forces the first end 60 of the beam to move in a vertical arc 64 rather than truly horizontally.
What remains needed in the art is a linkage which overcomes the aforesaid deficiency of a Scott-Russell linkage mechanism.
The present invention is a solid axle guidance linkage mechanism having a straight line movement which does not suffer from the movement deficiencies associated with either a track bar linkage or a Scott-Russell linkage mechanism.
The straight line linkage mechanism according to the present invention, (which may be referred to alternatively as either a xe2x80x9cChan-Cameron mechanismxe2x80x9d or a xe2x80x9cChan-Cameron linkage mechanismxe2x80x9d) includes a main bar, a tie rod and a shackle. The shackle is preferably configured as an xe2x80x9cA-armxe2x80x9d, having its legs pivotally connected to a solid axle. The apex of the shackle is pivotally connected to a first end of the main bar. The opposite second end of the main bar is pivotally connected to the frame. The tie rod is pivotally connected at one end to a mid-range location of the axle and, at its opposite end, pivotally to a mid-point location of the main bar. The connection locations of the main bar are spaced apart twice as far as the connection locations of the tie rod.
In operation, as the axle moves vertically relative to the frame in response to the wheels encountering irregular terrain, the first end of the main bar will tend to move horizontally. The shackle is mounted to the axle so that the apex thereof is horizontally movable. Accordingly, the axle is able to move vertically relative to the frame without a vertical arc component.
Accordingly, it is an object of the present invention to provide a straight line linkage mechanism for a solid axle.
This and additional objects, advantages, features and benefits of the present invention will become apparent from the following specification.